Field of the Invention
The present invention is directed to apparatus for the storage and retrieval of data and information. More particularly, it relates to improvements in apparatus for transporting information storage disks, for example, magnetic, optic and magneto-optic storage disks, in a storage and retrieval device commonly referred to as an automated disk library.
Automated disk libraries, also known as "juke-boxes", are known in the art for storing and accessing a large number of data storage disks. Examples of such libraries are those disclosed in U.S. Pat. Nos. 4,286,790, 4,502,133, 4,504,936 4,608,679, 4,614,474, 4,787,074 and 4,817,071. In such libraries, each information storage disk is housed in a protective cartridge or carrier which holds the disk and permits disk handling while permitting accessibility to the disk for data recording and/or retrieval. The disk carriers, with the associated disks, are supported by one or more storage racks which are arranged to support the disk and disk carriers in closely spaced parallel planes, for example, one above the other with the disks being disposed horizontally. Such automated disk libraries commonly include one or more disk drives for recording and/or retrieving information to or from a disk, as well as a disk carrier transport mechanism for transporting a selected carrier and disk between the storage location and the disk drive unit.
A necessary attribute of automated disk libraries is the ability to reliably transfer the disk from the storage rack to the transport means to the disk drive and back again. It is thus necessary that the transport means be repeatably and accurately aligned with the various stations that are addressed so that each disk is accurately aligned with the transport means, the storage station, or the disk drive, respectively, so that the transfer of the disk is repeatably and consistently reliable. To accomplish this repeatably accurate placement of the transport means, the transport means must be accurately located within the assembly and the accurate location must be the same for all positions of the transport means within the assembly. This accurate positioning must be with respect to all the three spatial dimensions, i.e., along the x-axis, the y-axis and the z-axis, as well as with respect to rotation of the transport means about each of the axis, i.e., rotation with respect to the x-axis, .theta..sub.x, with respect to rotation about the y-axis, .theta..sub.y, and rotation about the z-axis, .theta..sub.z.
In order to achieve the accurate and repeatable location of the transport member with respect to the various locations within the assembly, prior art automated disk libraries have been over-designed and overbuilt using expensive high-precision components that are costly in both size, weight and price to achieve the locating accuracy and repeatability necessary. Although the prior art automated disk libraries accomplish the desired result, they are heavy, oversized, and expensive, limiting their usefulness and acceptability. An example of this is seen in the transport mechanism locating means which consists of a pair of long, straight, round steel bars extending the length or height of the library. The transport mechanism is provided with two pairs of linear bushings which ride on the bars. The difficulties with such an arrangement include the necessity of utilizing high-precision bars that have the same diameter along the full length of the assembly. If the bars are not the same diameter throughout their length, the transport mechanism is too loose in some locations and too tight in others, interfering with proper operation and movement of the transport. Moreover, the linear bushings used must be of high precision and thus costly. Additional difficulties are found in the fact that the bushings must be colinear between the two riding the same bar. If they are not colinear, binding will occur, interfering with the operation of the entire automated disk library. In order to achieve colinearity it is necessary to use precision bushings and to accurately align them on the transport mechanism adding to the cost of the overall assembly. A further consideration of the prior art automated disk libraries is the fact that the use of the long steel bars as the guide rails for the transport mechanism in conjunction with the bushings prevents the support of the rails mid-span. Thus, transverse displacement of the rails and the resulting misalignment of the transport mechanism occurs because of the transverse loads applied to or by the transport mechanism as it is moved along the rails. As a result, heavier rods than would otherwise be expected must be used. Again, this adds to the cost and weight of the automated disk library.
It will be seen from the foregoing that automated disk libraries of the prior art are both bulky, heavy, expensive and expensive to operate and maintain. As a result, the information capacity of the library for a given volume of the library is limited by the bulk of the structure, while the market acceptance is limited by this and the cost thereof.
It will thus be seen that the provision of an automated disk library which provides the necessary rigidity and accuracy of positioning of the transport mechanism with respect to the storage bays and the disk drives without the attendant cost, bulk and weight of the prior art devices would be desirable from both cost and space considerations.